How to set ssl_trusted_certificate in OCSP Stapling?

I want to increase performance of my nginx using OCSP Stapling here:
=> %E2%80%93-Optimize-SSL/TLS

But In order to tun on OCSP Setting I need this in my nginx.conf:

ssl_stapling on;
ssl_stapling_verify on;
ssl_trusted_certificate /etc/nginx/cert/trustchain.crt;
resolver valid=300s;

My current certificate settings looks like this now:

ssl_certificate     %ssl_pem%;
ssl_certificate_key %ssl_key%;

My question is how to setup “ssl_trusted_certificate” which needed to enable ssl_stapling?

For information:
On backend: I use self signed certificate
On Frontend: I use Cloudflare SSL (Full mode)

Use Cloudflare orgin certificate instead SSL Certificates and Let's Encrypt — Hestia Control Panel documentation

Also ssl_stapling should already be enabled, check /etc/nginx/nginx.conf